The field of this invention relates to a substance which causes removal of urea from a liquid. This substance can be utilized in combination with an artificial kidney to effect removal of urea from the dialysate solution employed within the artificial kidney prior to the dialysate solution being reconducted through the artificial kidney as one of the various embodiments of the invention.
A common kidney disorder within animals is renal failure. Renal failure is when the kidneys are unable to carry on their normal function of excreting wastes and balancing the internal chemical environment of the body. Renal failure may occur abruptly as due to an obstruction of the urinary tract but most often develops gradually because of progressive destruction of renal tissue by disease. The end result of renal failure is that complete excretion of certain substances within the blood is no longer possible and their blood concentrations therefore rise.
One of the more important substances which it is necessary to remove from the blood is nitrogeneous waste such as urea.
Within recent years, it has been common to employ the use of an artificial kidney to partially replace the function of the natural kidney. Primarily, procedures using such artificial kidneys provide for the conducting of blood outside the body and across a semi-permeable membrane system with a saline solution passing on the other side of the membrane. The saline solution used in this procedure is known as "dialysate". The undesirable waste products within the blood are caused to pass through the membrane into the dialysate solution by a process known as dialysis. Normally, such artificial kidneys are employed upon human beings. Hereinafter, the use of such an artificial kidney will be described in relation to the human being although such artificial kidneys may be employed within lower order animals.
Once the dialysate solution has picked up the waste products of the blood, either the dialysate solution must be discarded or the concentration of the waste products must be reduced in the dialysate solution prior to the solution being recirculated through the artificial kidney. The dialysate solution in itself is relatively inexpensive. However, for a particular treatment which usually takes from 8 to 10 hours in time, between 50 and 100 gallons of the dialysate solution will be passed through the artificial kidney. The need for such a large volume of dialysate substantially increases the cost of each treatment, the complexity of required equipment, and the cost of the equipment installation. Therefore, it has been desirable to use only a small volume of the dialysate solution by reducing the concentration of the waste products therefrom and recirculating it back through the artificial kidney.
The most difficult waste material to remove from the dialysate solution is the nitrogenous type of waste material such as urea. A desirable way to effect the removal of urea from a dialysate solution has been described in U.S. Pat. No. 3,669,880 granted June 13, 1972. In this patent, the urea in the dialysate system is converted into ammonia carbonate by urease and the ammonium ion is thereafter picked up and replaced by sodium and hydrogen as the solution flows through zirconium phosphate.
It has been common in the past as taught in U.S. Pat. No. 3,669,880 to intermix the urease with diatomaceous earth (also known as diatomite). This material is defined as a light pliable siliceous material derived chiefly from diatom remains and used especially as a filter. The diatomite is intended to hold the urease within a fixed layer in its column. However, the diatomite does not make the urease completely insoluble in the liquid stream, and in the preferred embodiment described in U.S. Pat. No. 3,669,880 some small amount of urease could dissolve into the liquid and be carried through the column and into other regions of the recirculating system. Wherever the urease lodges it would act to convert the urea in the circulating liquid into ammonium carbonate at that site. In that embodiment this could result in measurable ammonia concentration levels downstream of the column.